Method and device for performing a leak test on a gas generator

ABSTRACT

The invention relates to a method for performing a leak test on a gas generator ( 1 ), especially for airbags, according to which: the gas generator ( 1 ) is filled with a pressurized gas mixture, among other things, helium; the gas generator ( 1 ) filled with the gas mixture is introduced into a test chamber ( 2 ); gas is evacuated from the test chamber ( 2 ); the amount of helium exiting from a possibly present leak is determined with the aid of a sensor, and; the signal furnished by the sensor is used for determining the tightness/leakage of the gas generator ( 1 ). In order to accomplish the goal of performing a cost-effective search for leaks, the invention provides that the gas generator ( 1 ) is filled with a gas mixture whose helium proportion is equal to at least 50%.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to a method forperforming leak tests, and particularly to a method for performing leaktests on a gas generator.

[0003] 2. Technical Background

[0004] Gas generators, such as those employed as air bags, must meetstringent safety standards for obvious reasons. Before their deploymentthey are analyzed for leaks. Leakage typically must not exceed 10⁻⁸mbar/s. The service life of air bags, for example, is of particularconcern.

[0005] In one approach that has been considered, helium gas is injectedinto the gas generator for the purpose of integrally searching hollow,enclosed items for the presence of leaks. This is performed byintroducing (injecting or bombing) helium at a low concentration beforethe test object is sealed or by exposing the test object in advance of aleak test to helium at high pressure. In other words, the gas generatoris filled with a compressed gas (commonly CO₂) which includes arelatively small quantity of helium. Should a leak be present, a smallquantity of helium will penetrate into the interior of the test object(gas generator). After the test object is exposed to the gas, it isdisposed in a test chamber. A leak test is performed by evacuating thechamber to a specific predetermined pressure. If there is a leakpresent, a part of the helium present at a low concentration in theinterior of the test object will migrate into the test chamber. Thehelium is detected with the aid of the sensor, commonly a massspectrometer.

[0006] There are drawbacks to the above described approach. In order toattain the detection limits of this magnitude, it is required toevacuate the test chamber after having introduced the test object torelatively low pressures. In order to attain this goal, vacuum pumpscapable of attaining sufficiently low base pressures need to beemployed. In addition, there exists in the manufacture of gas generatorsthe requirement of short cycle times. These can only be attained whenthe employed vacuum pumps offer, in addition, a high pumping capacity.For this reason leak detection instruments must necessarily employrelatively expensive pump systems capable of meeting the low basepressure requirements and high pumping capacities.

[0007] There are other drawbacks as well. Highly sensitive sensors mustbe employed to detect the very small amounts of helium present in thetest chamber in the event of a leak in the wall of the gas generator.Currently, expensive mass spectrometers are being used to perform thistask.

[0008] Thus, it is desirable to provide a cost effective method forperforming high-sensitivity leak searching on gas generators, air bagsin particular.

SUMMARY OF THE INVENTION

[0009] The present invention addresses the problems and needs describedabove. The method and apparatus of the present invention provide a costeffective method for performing high-sensitivity leak searching on gasgenerators, such as air bags. The present invention relates to a methodfor performing a leak test on a gas generator, and is especiallyapplicable to airbags. The gas generator is filled with a pressurizedgas mixture that includes, among other things, helium. The gas generatoris filled with the gas mixture and introduced into a test chamber. Thegas is evacuated from the test chamber. The amount of helium exitingfrom a possibly present leak is determined with the aid of aninexpensive sensor. The signal furnished by the sensor is used fordetermining the tightness/leakage of the gas generator. Moreover, thepresent invention relates to a device suited for performing said method.

[0010] One aspect of the present invention is a method for performing aleak test on a gas generator. The method includes the steps of fillingthe gas generator with a pressurized gas mixture that includes helium,e.g., the gas generator is filled with a gas mixture whose heliumproportion is equal to at least 50%. The gas generator (1) is introducedinto a test chamber (2). The gas mixture is evacuated from the testchamber (2). An amount of helium is sensed exiting from a possiblypresent leak with a sensor device. The sensor is configured to provide asensor signal. The amount of helium exiting from the possibly presentleak is determined from the signal furnished by the sensor.

[0011] In another aspect, the present invention includes a method forperforming a leak test on a gas generator. The method includes the stepsof filling the gas generator with a pressurized gas mixture thatincludes helium, e.g., the gas generator is filled with a gas mixturewhose helium proportion is approximately 100%. The gas generator isintroduced into a test chamber. The gas mixture is evacuated from thetest chamber. An amount of helium is sensed exiting from a possiblypresent leak with a sensor device. The sensor is configured to provide asensor signal. The amount of helium exiting from the possibly presentleak is determined from the signal furnished by the sensor.

[0012] In yet another aspect, the present invention includes anapparatus for performing a leak test on a gas generator. The apparatusincludes a gas source configured to fill the gas generator with apressurized gas mixture that includes helium. The gas mixture includes ahelium proportion equal to at least 50%. A test chamber is configured toaccommodate the gas generator. The test chamber includes at least oneflexible wall. A gas evacuation mechanism is configured to evacuate thegas mixture from the test chamber (2). A sensor is configured todetermine an amount of helium exiting from a possibly present leak. Thesensor provides a signal corresponding to a measurement of thetightness/leakage of the gas generator. An analyzer is coupled to thesensor. The analyzer is configured to determine the tightness/leakage ofthe gas generator based on the signal received from the sensor.

[0013] Additional features and advantages of the invention will be setforth in the detailed description which follows, and in part will bereadily apparent to those skilled in the art from that description orrecognized by practicing the invention as described herein, includingthe detailed description which follows, the claims, as well as theappended drawings.

[0014] It is to be understood that both the foregoing generaldescription and the following detailed description are merely exemplaryof the invention, and are intended to provide an overview or frameworkfor understanding the nature and character of the invention as it isclaimed. The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate various embodimentsof the invention, and together with the description serve to explain theprinciples and operation of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a cross-sectional view of the test apparatus.

DETAILED DESCRIPTION

[0016] Reference will now be made in detail to the present exemplaryembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.An exemplary embodiment of the apparatus of the present invention isshown in FIG. 1, and is designated generally throughout by referencenumeral 10.

[0017] In accordance with the invention, the present invention isdirected to a method for performing a leak test on a gas generator. Themethod includes the steps of filling the gas generator with apressurized gas mixture that includes helium, e.g., the gas generator isfilled with a gas mixture whose helium proportion is equal to at least50%. The gas generator (1) is introduced into a test chamber (2). Thegas mixture is evacuated from the test chamber (2). An amount of heliumis sensed exiting from a possibly present leak with a sensor device. Thesensor is configured to provide a sensor signal. The amount of heliumexiting from the possibly present leak is determined from the signalfurnished by the sensor. Thus, the present invention addresses theproblems and needs described in the Background Section. The method andapparatus of the present invention provide a cost effective method forperforming high-sensitivity leak searching on gas generators, such asair bags.

[0018] As embodied herein, and depicted in FIG. 1, the leak testapparatus 10 includes foil test chamber 2. Foil test chamber includes aframe construction (frames 3 and 4). Foils 5 and 6 are shown as beingclamped by frame 3 and frame 4. Foil 5 and foil 6 are flexible wallmembers. The foils 5 and 6 are equipped in the area of the test object 1with porous foil sections 7, 8, which allow for a contiguousintermediate space 11 between the foils 5 and 6 on the one hand, and thetest sample 1 on other hand. The drawing figure depicts a gas generator1 containing at least 50% helium. The gas generator being filled by agas source which is not shown for clarity of illustration. The gasgenerator was introduced into a foil test chamber 2.

[0019] In order to create the necessary test chamber 12 for leaksearching the test object 1, the space between the foils 5, 6 isevacuated. Thus the foils 5 and 6 rest flush against the test object 1thereby forming the test chamber 12 comprising intermediate space 11,formed by means 7, 8, and the volume of the test object 1.

[0020] The test chamber is evacuated through a central connection 13,which may be designed by way of a hose connection 14, for example, andwhich is joined to line I 18. The means 7, 8 forming the intermediatespace do not extend in to the rim area of the foils 5, 6 so that theouter seal of the test chamber is performed in that the foils 5, 6 restat their rim areas immediately flush against each other as soon as theevacuation commences. Further evacuation and the leak test is performedthrough the connection 13.

[0021] In the test chamber 12 a pressure is created which issufficiently low to allow—in the instance of a leak—the test gas to beejected from within the test object 1. The test gas is detected by aninexpensive detector sensitive to the test gas. The detector isconnected at the intermediate space 11/test chamber 12. Thedetector/sensor 20 is connected to an analyzer 30. Sensor 20 transmits asignal to analyzer 30. The signal measures the amount of helium exitingfrom a possible leak that may be present. Thus, the signal correspondsto a measurement of the tightness/leakage of the gas generator (1). Theanalyzer is configured to determine the tightness/leakage of the gasgenerator (1) based on the signal received from the sensor. The analyzermay be resident on any suitable computing device (not shown). Those ofordinary skill in the art will recognize that the computing device isalso coupled to a user interface which allows a user to view the resultsof the test.

[0022] In that the helium concentration in the gas generator to betested is high, there is in the instance of a leak in the wall of thegas generator more helium present for determining the presence of theleak. In order to attain the demanded detection limits, pumps having alower compression and/or lower pumping capacity may be employed. Fastercycle times can be attained. In all, there result through the presentinvention considerable cost related benefits.

[0023] Not only with respect to leak searching has it been found to beadvantageous when the helium proportion in the gas mixture of the gasgenerator according to the present invention amounts to between 80% andalmost 100%, preferably between 90% and almost 100%. Its is especiallyadvantageous when the gas generator is filled exclusively with helium.Moreover, it is expedient within the scope of the present invention toemploy for the purpose of performing the leak search, a test chamberequipped with at least one flexible wall. In the employment of such testchambers, the dead volume of the test chamber—test chamber volume afterevacuation and during the helium detection process—is minimized. Thusthe required pumping capacity can additionally be further significantlyreduced and further cost advantages attained.

[0024] It will be apparent to those skilled in the art that variousmodifications and variations can be made to the present inventionwithout departing from the spirit and scope of the invention. Thus, itis intended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method for performing a leak test on a gasgenerator (1), comprising: filling the gas generator (1) with apressurized gas mixture that includes helium, wherein the gas generator(1) is filled with a gas mixture whose helium proportion is equal to atleast 50%; introducing the gas generator (1) into a test chamber (2);evacuating the gas mixture from the test chamber (2); sensing an amountof helium exiting from a possibly present leak with a sensor device, thesensor being configured to provide a sensor signal; and determining theamount of helium exiting from the possibly present leak from the signalfurnished by the sensor.
 2. The method in accordance with claim 1,wherein the helium proportion is between 80% and 100%.
 3. The method ofclaim 2, wherein the helium proportion is substantially between 90 andapproximately 100%.
 4. The method of claim 1, wherein the gas generatorincludes an airbag.
 5. The method in accordance with claim 1, whereinthe test chamber (2) includes at least one flexible wall (5, 6).
 6. Amethod for performing a leak test on a gas generator, the methodcomprising: filling the gas generator (1) with a pressurized gas mixturethat includes helium, wherein the gas generator (1) is filled to 100%with helium; introducing the gas generator (1) into a test chamber (2);evacuating the gas is evacuated from the test chamber (2); sensing anamount of helium exiting from a possibly present leak with a sensordevice, the sensor being configured to provide a sensor signal; anddetermining the amount of helium exiting from the possibly present leakfrom the signal furnished by the sensor.
 7. The method in accordancewith claim 6, wherein the test chamber (2) includes at least oneflexible wall (5, 6).
 8. The method in accordance with claim 7, whereinthe leak test is performed in a foil test chamber.
 9. An apparatus forperforming a leak test on a gas generator (1), the apparatus comprising:a gas source configured to fill the gas generator (1) with a pressurizedgas mixture that includes helium, the gas mixture including a heliumproportion equal to at least 50%; a test chamber (2) configured toaccommodate the gas generator (1), the test chamber including at leastone flexible wall (5,6); a gas evacuation mechanism configured toevacuate the gas mixture from the test chamber (2); a sensor fordetermining an amount of helium exiting from a possibly present leak,the sensor providing a signal corresponding to a measurement of thetightness/leakage of the gas generator (1); and an analyzer coupled tothe sensor, the analyzer being configured to determine thetightness/leakage of the gas generator (1) based on the signal.
 10. Theapparatus of claim 9, wherein the gas generator is filled with a gasmixture including a helium proportion that amounts to at least 50%. 11.The apparatus of claim 10, wherein the helium proportion is between 80%and 100%.
 12. The apparatus of claim 11, wherein the helium proportionis substantially within a range between 90% and approximately 100%. 13.The apparatus of claim 10, wherein the helium proportion isapproximately 100%.
 14. The apparatus of claim 9, wherein the gasgenerator includes an airbag.
 15. The apparatus of claim 9, wherein theat least one flexible wall (5,6) includes a plurality of flexible walls.